I dont know about you guys, but I have noticed that my car runs louder and rougher when filling up with 40 cetane diesel fuel. I've been lucky enough to have a local gas station (Liberty Fuels) that sold 45 cetane fuel close enough to my house, but they recently downgraded back down to 40.

After doing some research, I've found that there are a few stations out there that sell "premium diesel" with either 47 or 50 cetane ratings. Today, I checked our a relatively local BP station and to my surprise, they did carry 47 cetane diesel for $4.09 a gallon. After filling up, I noticed that the car ran so much smoother and quieter. The difference between 40 and 47 is night and day.

Next step: finding a station that carries 50. Has anyone seen 50 cetane rated diesel at any major retailers (Exxon, BP, Sunoco, etc.)? Or, to those local to the MD/DC/NOVA area, any stations or highway truck stops?

It's hard to tell what the exact cetane content is at most pumps since the label only states the min required by the govt, which is 40 cetane. Our cars are tuned for 50 but will run on 40 with some adverse effects, such as louder knock, reduced mpg, loss in hp etc. It doesn't hurt your engine it's just not running at its optimum.

Good luck finding a station in VA or MD that sells 50 cetane. If/when you find one let me know. Shell is the best bet locally for a quality high cetane content diesel. The last Shell I filled up at in Chantilly sold 46+ cetane.

Was out of town (Charlottesville VA) and filled up at a BP/Amaco with 47 Cetane lable on the pump and drove 350 miles. Made zero difference that I could tell from the Hess diesel with no cetane lable on the pump I have been using all along. I suspect it really was not 47. Car seems to be very consistant with 40 MPG on the highway with AC on, about 41 with AC off (light right foot, running about 75 MPH).

I conversed with these guys (SynDiesel) a couple of months ago because I was planning to buy a small amount before going to the track. Not only is it VERY expensive, which makes it almost economically impractical, but you should also be aware there are NO lubricity additives in this fuel. It is designed to be combined with regular diesel a supplemental lubricity addtive. Really meant for track use.

Haven't seen premium advertised in my area. You shouldn't notice a mpg difference on highway trip but it may idle less smoothly and it may take longer to warm up (suspect non-issue with summer weather fast approaching ). Many of the euro guys experience lower mpg's on diesel with cetane over 50-55.

I conversed with these guys (SynDiesel) a couple of months ago because I was planning to buy a small amount before going to the track. Not only is it VERY expensive, which makes it almost economically impractical, but you should also be aware there are NO lubricity additives in this fuel. It is designed to be combined with regular diesel a supplemental lubricity addtive. Really meant for track use.

Expensive I don't care about if I am going to the track. It would only be like 5 gallons. As far a lubricity additives, I didn't know it lacked that completely.

So if it has to be mixed with regular diesel, how can one figure out the best ratio? 50/50? 60/40? 75/25?

Expensive I don't care about if I am going to the track. It would only be like 5 gallons. As far a lubricity additives, I didn't know it lacked that completely.

So if it has to be mixed with regular diesel, how can one figure out the best ratio? 50/50? 60/40? 75/25?

I'd like to see if it helps on the dyno too, out of curiosity.

Correct there are NO lubricity additives, so use with discretion. I agree it appears to be a fine product for track days, just not economically practical IMO for daily use.

SynDiesel can advise on the ratios, but based on experiences by others using this product on TDI Club forums and in particular one long term user who uses it for autox events, and if I recall correctly he mixed it 50/50 with regular diesel along with a lubricity additive. No dynos that I am aware of but the long term user on TDI forum did say he saw his lap times come down a couple of points which made him a believer.

At my last fill up, the label actually did say 47. Based on that, they couldn't legally sell anything less than 47, correct?

Correct which is why I said at "most" stations, because most stations only label the miniumum required by the govt in which case it's hard to tell if one is getting 40 or 45. However I have been to some stations including the Shell in Chantilly where the pump stated a min 46. I suspect the Shell I frequent sells higher cetane fuel than 40 despite the pump states min cetane rating of 40.

Anecdotally, I've been using Chevron almost exclusively for the past year; my calculated MPG ranges between 27.8 and 28.5 per tank with mixed driving. On a whim I filled up with Exxon diesel a couple weeks ago, and I turned up 29.6mpg on that tank. Maybe a fluke, and that's just one data point, but I'm running another tank of Exxon now so we'll see how that goes.

I've only seen one station in my area that advertises "premium diesel", and it's a Shell station. I highly doubt they get different fuel than all the other shell stations though.